The major goal of the proposed research is to determine the neuronal basis of simple forms of learning. We plan to study food-aversion learning in a gastropod Mollusc such as the snail, Helisome trivolvis. A subsidiary goal is to develop optical methods for monitoring neuron activity. We can now monitor activity in about 100 cells simultaneously. We propose to develop the technique further so that 200-300 neurons could be monitored. While we hope that such an apparatus will facilitate the investigation of the neuronal basis of simple kinds of learining, it is expected that conventional electrophysiological techniques would also be extensively used.